A resin sheet for interlayer adhesion between circuit boards in a multilayer circuit board frequently used in electric devices has a three layer structure of a passivation layer, a resin layer and a release layer, and is generally produced by a continuous process. A product is cut into sheets or wound as rolls with a predetermined length which are then released as commercial products. In a general use, one release sheet is removed, the resin layer is disposed such that it faces the circuit board and these are laminated, and then the passivation layer is removed.
Generally, when a resin material is continuously applied to the passivation layer to form a resin layer, the resin material is sometimes applied in an area narrower than the sheet width of the passivation layer (for example, see Patent Document No. 1). This is because when the resin material is soft and fluid, a pressure applied to the resin layer may make the circumferential resin layer flowing to the edge of the passivation layer and further running out. Therefore, the edges of the passivation layer in a sheet width direction which are left uncoated prevent the resin layer from running out to the surrounding area.
When such running out to the area surrounding the resin layer occurs, the resin tends to be thinner than the other regions. Thus, when the resin sheet is adhered to an adherend, a resin layer having a sufficient thickness for adhesion may not be ensured.
On the other hand, for a resin layer with a less amount of running out such as a so-called hard coat layer, a resin material is applied to an area narrower than the sheet width of the passivation layer, and after the application, both sides are cut and removed by a predetermined size (for example, see Patent Document No. 2). This is because the resin layer applied to the end faces tends to be thicker than the other regions due to difference in surface tension balance of the applied solution on the edges, and thus continuous winding causes raise of the periphery, that is, a “derby hat” phenomenon. Therefore, after application of the resin material, both sides (lugs) of the sheet are cut and removed using, for example, a ring cutter.
However, with the passivation layer and the resin layer having the same width, the equality in width can make it difficult to remove the passivation layer after laminating the adhesion sheet on, for example, a circuit board surface or cause damage to the peripheral resin layer. Such damage can lead to contamination with a part of the broken resin layer as a foreign material, adversely affecting a product yield.
Patent Document No. 1: Japanese published unexamined application No. 1999-092725.
Patent Document No. 2: Japanese published unexamined application No. 2006-212549.